1. Field of the Art
The present invention relates in general to a composite ceramic structure and a method of manufacturing the same, and more particularly to an improved technique for producing such a composite ceramic structure, by first preparing a formed ceramic piece which constitutes a portion of the composite ceramic structure, then forming a mass of ceramic powder which constitutes the remaining portion of the structure such that the formed powder mass is integral with the previously prepared ceramic piece, and finally firing the formed mass of ceramic powder.
2. Related Art Statement
Silicon nitride, silicon carbide and other silicon ceramics, and ceramic materials, such as cordierite, having a low coefficient of thermal expansion are excellent in resistance to heat and thermal shock. Recently, such ceramic materials have been drawing increasing attention of the industry, as materials suitable for structural components such as gas turbines, and parts for internal combustion engines, that are used in high-temperature environments.
Generally, structural components like engine parts are complicated in construction. Therefore, it is almost impossible to produce such structural components by means of finishing, as with a grinder, fired or sintered blanks of simple configuration, e.g., in the form of rods or rectangular blocks made of fine particles of silicon nitride or silicon carbide. Further, it is extremely difficult to obtain structural components of a complicated configuration in a single molding operation. The use of these manufacturing processes is difficult particularly when the required physical properties such as strength of a ceramic structure to be produced are different from one portion to another.
In view of the above difficulties, it has been attempted to produce a composite ceramic structure by joining together two or more originally separate ceramic pieces, which are formed of suitably selected ceramic materials that meet the specific physical requirements of the respective portions of the composite structure. These separate ceramic pieces are formed in shapes corresponding to the shapes of the individual portions of the composite structure, and are joined together into the composite ceramic product, namely, an end product. For example, a method of producing such a composite ceramic structure is disclosed in Japanese Patent Application which was published in 1978 for opposition purpose under Publication No. 53-38722. This method is used to produce a rotor for an axial-flow turbine. The method comprises the steps of: preparing a vane or blade portion of the rotor with a reaction-sintered silicon nitride; placing the prepared vane portion in a mold of a hot press; and forming a rotor portion of the rotor by hot pressing, as an integral part of the vane portion. Other methods appear in Japanese Patent Applications laid open in 1980 under Publication Nos. 55-134701 and 55-161902, and Japanese Patent Application laid open in 1982 under Publication No. 57-88201. In these methods, a vane portion of a rotor is formed with an axial hole for connection to a shaft portion of the rotor which is separately prepared. The shaft portion is inserted in the axial hole, and the shaft portion and the vane portion are joined together with a suitable bonding agent, whereby a one-piece rotor structure is obtained.